1. Field of the Invention
The present invention relates to an acoustic wave device used in, for example, portable terminals, and to a filter and a duplexer using the same.
2. Background Art
FIG. 14 is a partial sectional view showing a conventional acoustic wave device. Conventional acoustic wave device 1 includes piezoelectric substrate 2, IDT (Inter Digital Transducer) electrode 3 provided on piezoelectric substrate 2, and dielectric layer 4 provided on piezoelectric substrate 2 so as to cover IDT electrode 3. Furthermore, conventional acoustic wave device 1 includes extraction electrode 5 connected to IDT electrode 3 and extracted onto dielectric layer 4, bump 6 provided on extraction electrode 5 via metal layer 6a, and protective layer 7 provided on dielectric layer 4 so as to cover extraction electrode 5.
A thermal shock may be applied in a state in which acoustic wave device 1 is mounted on a mount board (not shown) by bump 6. At that time, a thermal stress due to a difference between the thermal expansion coefficient of acoustic wave device 1 and the thermal expansion coefficient of the mount board is transmitted to piezoelectric substrate 2 via bump 6 and metal layer 6a and through extraction electrode 5 and dielectric layer 4. As a result, a stress is applied to piezoelectric substrate 2, thus causing cracks in piezoelectric substrate 2.
In particular, when extraction electrode 5 is routed on the upper surface of dielectric layer 4 to form an inductance, since a contact area between extraction electrode 5 and dielectric layer 4 is increased, cracks may easily occur in piezoelectric substrate 2.